1. Field of the Invention.
The present invention relates to engine lubricating oil generally and, more particularly, but not by way of limitation, to a novel system for indicating the need to change the engine lubricating oil.
2. Background Art.
Engine oil must be changed periodically to remove products of combustion that would damage the engine if such materials were allowed to accumulate over a relatively long period of time. Traditionally, engine oil was changed whenever the vehicle reached a predetermined mileage. Oftentimes, the vehicle manufacturer may suggest that the engine oil be changed more frequently if harsh driving conditions exist or if the engine oil has not been changed for some period of time. It is a relatively simple matter to rely on vehicle mileage to determine when to change the engine oil; however, the latter two situations require the operator of the vehicle to make a judgement as to when to change the engine oil. This judgement is really a guess, since the operator has no physical data on which to base the judgement. Unfortunately, guessing when to change the engine oil may result in changing the engine oil more frequently than is necessary, resulting in unnecessary expense, or, worse, not changing the oil frequently enough, resulting in shortened engine life.
There have been a number of attempts to provide more accurate indications that engine oil should be changed.
U.S. Pat. No. 3,723,964, issued Mar. 27, 1973, to Lace, and titled ENGINE CONDITION MONITORING APPARATUS, describes a system that produces two electrical signals representing engine oil pressure corrected for temperature and engine temperature corrected for ambient temperature and a third electrical signal representing engine speed. The first two signals are compared with the third signal and warnings given if either or both exceeds the third.
U.S. Pat. No. 3,859,626, issued Jan. 7, 1975, to Baratti, and titled VEHICLE ENGINE OIL TEMPERATURE PRESSURE AND METAL DETECTING DEVICE, describes a sensor that is screwed into the port which would otherwise receive the oil pressure switch. The sensor activates a light, which may be on the dashboard of the vehicle if the oil pressure is low, the oil temperature is high, or metallic particles are present.
U.S. Pat. No. 4,007,629, issued Feb. 15, 1977, to Hochstein, and titled METHOD AND APPARATUS FOR MONITORING OIL DEGRADATION, describes a method and apparatus for monitoring oil degradation which includes a "creep" material sensor that is in contact with the oil to act as an analog computer, in that the creep material changes in length in response to the temperature of the oil and the time at that temperature. The output of that sensor is summed with the output of a second sensor which computes the number of times the oil is heated to a temperature lower than the temperature required to disperse the oil, water, acid, and sludge contaminating the oil.
U.S. Pat. No. 4,551,703, issued Nov. 5, 1985, to Bourauel et al., and titled SERVICE INTERVAL SIGNALLING DEVICE FOR PRIME MOVERS, describes a system that provides a maintenance service interval signal based on the total number of revolutions of a rotary part of the prime mover and optionally one or more of (1) magnitude of load, (2) temperature of an operating fluid, (3) fuel consumption rate, and (4) time intervals.
U.S. Pat. No. 4,629,334, issued Dec. 16, 1986, to Hochstein, and titled ENGINE AND TRANSMISSION OIL DEGRADATION AND TEMPERATURE MONITOR, describes an engine or transmission oil degradation monitor that measures the change in resistivity of the oil corrected by temperature.
U.S. Pat. No. 4,677,847, issued Jul. 7, 1987, to Sawatari et al., and titled AUTOMOTIVE ENGINE OIL MONITORING SYSTEM, describes an engine oil deterioration monitor which provides a continuous output signal representing the remaining useful life, in terms of time or vehicle mileage, of the oil as a function of oil temperature or speed of the engine.
U.S. Pat. No. 4,706,193, issued Nov. 10, 1987, to Imajo et al., and titled OIL DEGRADATION WARNING SYSTEM, describes a monitor that provides a warning signal when motor oil is to be changed, the signal being based on degradation factors integrated over time, and the warning signal being postponed when oil is added. The degradation factors include (1) moved distance, (2) oil temperature, (3) engine speed, and (4) type of oil. In one embodiment, sensing lack of oil assumes an oil change and resets the system. In another embodiment, opening the hood and sensing lack of oil assumes an oil change. In a further embodiment, activation of a switch in the filler cap and low oil level assumes an oil change.
U.S. Pat. No. 4,742,476, issued May 3, 1988, to Schwartz et al., and titled AUTOMATIC ENGINE OIL CHANGE INDICATOR SYSTEM, describes a method of indicating when engine oil should be changed which computes an effective usage amount in relation to a measure of the actual engine usage and a penalty factor which operates to increase the effective usage amount when the engine operating conditions tend to cause an increased degradation of the engine oil, the penalty factor being determined as a sole function of the engine oil temperature. When accumulated computations reach a predetermined level, the operator is so advised.
U.S. Pat. No. 4,796,204, issued Jan. 3, 1989, to Inoue, and titled OIL DEGRADATION WARNING SYSTEM, describes an engine oil monitor that integrates oil temperature, engine speed, and engine load over time and provides an output indicating when at least one of the factors exceeds a predetermined value.
U.S. Pat. No. 4,847,768, issued Jul. 11, 1989, to Schwartz et al., and titled AUTOMATIC ENGINE OIL CHANGE INDICATOR SYSTEM, describes a method of indicating when engine oil should be changed based on equations which are combinations of engine operating parameters including a temperature term, without direct measurement of the engine temperature.
U.S. Pat. No. 4,862,393, issued Aug. 29, 1989, to Reid et al., and titled OIL CHANGE INTERVAL MONITOR, describes a diesel engine oil monitor that combines oil temperature, fuel flow, and volume of oil added to the engine since the last fuel change to compute the percentage of oil life used since the last oil change.
U.S. Pat. No. 5,060,156, issued Oct. 22, 1991, to Vajgart et al., and titled METHOD AND APPARATUS FOR DETERMINING ENGINE OIL CHANGE INTERVALS ACCORDING TO ACTUAL ENGINE USE, describes a monitor which calculates when the engine oil is exhausted by multiplying each spark plug pulse by weighting factors that are periodically determined by sampling engine oil temperature and length of time the engine has been in continuous use above a predetermined speed.
U.S. Pat. No. 5,382,942, issued Jan. 17, 1995, to Raffa et al., and titled ENGINE OIL MONITORING SYSTEM HAVING AN IN-VEHICLE DISPLAY OF THE CURRENT STATUS OF THE OIL, describes an oil monitoring system that calculates and displays as remaining percent oil life (1) the remaining percent tachometer oil life, (2) remaining percent time oil life, and (3) remaining percent odometer oil life. The system receives as an input the type of fuel and may include an oil dielectric constant sensor.
U.S. Pat. No. 5,633,796, issued May 27, 1997, to Cullen et al., and titled METHOD AND APPARATUS FOR INFERRING ENGINE OIL TEMPERATURE FOR USE WITH AN OIL CHANGE INDICATOR, states that the use of an oil temperature sensor adds cost and is not always accurate. Accordingly, in the described system, an electronic engine controller infers the instantaneous temperature of engine oil from other factors and then determines an oil change interval as a function of inferred oil temperature and the number of engine revolutions. A steady state oil temperature value is determined as a function of engine speed and aircharge, an oil temperature time constant is determined as a function of mass air flow rate, and the instantaneous oil temperature is determined as a function of the steady state oil temperature and the oil temperature time constant.
Most of the foregoing systems are complicated and relatively costly and none is easily and quickly retrofittable to an existing engine.
Accordingly, it is a principal object of the present invention to provide an engine oil change indicator system that is simple.
It is a further object of the invention to provide such a system that is economical.
It is an additional object of the invention to provide such a system that is easily and quickly retrofittable to an existing engine.
Other objects of the present invention, as well as particular features, elements, and advantages thereof, will be elucidated in, or be apparent from, the following description and the accompanying drawing figures.